Function to query specific repeated data in the table in sql

SQL functions for querying specific duplicate data in a table include: COUNT function: Counts the number of duplicate values. GROUP BY clause: Group data and calculate the values ​​in each group. HAVING clause: Filters the results of aggregate queries.

Function to query specific repeated data in the table in SQL

COUNT function

The COUNT function counts the number of duplicate values ​​in a table. Syntax:

<code class="sql">COUNT(column_name)</code>

Example:

To count the number of occurrences of "New York" in the "city" column in the "customers" table:

<code class="sql">SELECT COUNT(city) FROM customers WHERE city = 'New York';</code>

GROUP BY clause

The GROUP BY clause groups data and then applies an aggregate function (such as COUNT) to calculate the values ​​in each group. Syntax:

<code class="sql">SELECT column_name, COUNT(*)
FROM table_name
GROUP BY column_name</code>

Example:

To find out the number of customers grouped by city in the "customers" table:

<code class="sql">SELECT city, COUNT(*) AS customer_count
FROM customers
GROUP BY city;</code>

HAVING Clause

HAVING clause filters the results of an aggregate query. Syntax:

<code class="sql">SELECT column_name, COUNT(*)
FROM table_name
GROUP BY column_name
HAVING COUNT(*) > value</code>

Example:

To find the cities with more than 500 customers in the "customers" table:

<code class="sql">SELECT city, COUNT(*) AS customer_count
FROM customers
GROUP BY city
HAVING customer_count > 500;</code>

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